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arXiv 1606.08481math.AP
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三维Euler方程Lagrange修正的有限时间爆破

Finite time blowup for Lagrangian modifications of the three-dimensional Euler equation

Terence Tao

摘要:

在微分几何语言中,不可压缩无粘欧拉方程可以写成涡矢势形式的\begin{align*} \partial_t ω+ {\mathcal L}_u ω&= 0\\ u &= δ\tilde η^{-1} Δ^{-1} ω\end{align*},其中$ω$是涡量$2$形式,${\mathcal L}_u$表示关于速度场的李导数,$u$,$Δ$是Hodge Laplacian,$δ$是余微分。$\tilde η^{-1}$是由欧几里德度量$η$诱导的从$2$ -形式到$2$ -向量场的典范映射。在本文中,我们考虑了这些欧拉方程在三维空间的推广,其中的矢量位算子$\tilde η^{-1} Δ^{-1}$被替换为一个更一般的运营商$A$的顺序$-2$,这保留了拉格朗日结构的欧拉方程,以及其大部分的守恒律和局部存在理论。尽管如此,我们给出了三种不同的结构,这样一个运营商$A$承认光滑的解决方案,在有限时间内爆破,包括一个例子${\bf R}^3$这是自伴和正定。这表明了建立三维欧拉方程的全局正则性的障碍,因为任何这样的方法都必须使用这些方程的某些属性,而这些属性不是这里考虑的广义欧拉方程所共有的。

英文摘要:

In the language of differential geometry, the incompressible inviscid Euler equations can be written in vorticity-vector potential form as \begin{align*} \partial_t ω+ {\mathcal L}_u ω&= 0\\ u &= δ\tilde η^{-1} Δ^{-1} ω\end{align*} where $ω$ is the vorticity $2$-form, ${\mathcal L}_u$ denotes the Lie derivative with respect to the velocity field $u$, $Δ$ is the Hodge Laplacian, $δ$ is the codifferential (the negative of the divergence operator), and $\tilde η^{-1}$ is the canonical map from $2$-forms to $2$-vector fields induced by the Euclidean metric $η$. In this paper we consider a generalisation of these Euler equations in three spatial dimensions, in which the vector potential operator $\tilde η^{-1} Δ^{-1}$ is replaced by a more general operator $A$ of order $-2$; this retains the Lagrangian structure of the Euler equations, as well as most of its conservation laws and local existence theory. Despite this, we give three different constructions of such an operator $A$ which admits smooth solutions that blow up in finite time, including an example on ${\bf R}^3$ which is self-adjoint and positive definite. This indicates a barrier to establishing global regularity for the three-dimensional Euler equations, in that any such method must use some property of those equations that is not shared by the generalised Euler equations considered here.

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